On the taxonomy of Littorina africana (Mollusca: Gastropoda)

L. africana and L. knysnaensis are regarded as two morphs of a single species which exhibits a genetic cline along the south-eastern coast of southern Africa. The dark brown morph knysnaensis dominates the western, cooler end of the cline and is replaced by the pale blue morph africana at the warmer end of the cline. These conclusions are based on evidence from the latitudinal distributions, the complete range of intermediate forms regarding shell colour and shell morphology and the lack of differences in redular morphology, penial morphology or habitat.     

The Function of Male Dominance in the Eusocial Wasp, Mischocyttarus mastigophorus (Hymenoptera: Vespidae)

Males of a Neotropical eusocial wasp, Mischocyttarus mastigophorus , are dominant over their female nest mates. Mischocyttarus mastigophorus males behave aggressively toward females, while females rarely bite or chase males. Aggressive interactions between the sexes are behaviorally indistinguishable from dominance interactions among females. Males are long-lived as adults, and can reside on nests for periods of at least one month. Furthermore, males comprise a large proportion of post-emergence colony populations throughout much of the colony cycle. Males on the nest perform maintenance tasks at low rates, but contribute little other labor to their colonies. Males do not forage, but consume a disproportionate amount of the food (nectar and insect prey) collected by workers. Males in some colonies direct disproportionate amounts of aggression toward their queens, which may further contribute to males' food procurement. These data suggest that adult males represent a considerable energetic and labor cost to their colonies. I hypothesize that the dominance structure of M. mastigophorus directs food resources to adult males, with the function of increasing their longevity. Increased male longevity may be selectively advantageous in tropical species such as M. mastigophorus that found new colonies throughout much or all of the year. When females initiate new nests over much of the year, individual males' mating opportunities may be temporally distributed, favoring longer adult lifespans. Male dominance is predicted to occur in other populations of independent-founding Neotropical Polistinae with asynchronous colony foundation.     

Female Colour Polymorphism: Gender and the Eye of the Beholder in Damselflies

Damselflies provide a classic example of female colour polymorphism. Usually, one female morph resembles the blue male colour (andromorph) while one, or more, female morphs are seen as typically female (gynomorph). Damselfly species fall in two distinct groups with respect to recent developments in mimicry theory: in some species females are perfect, they match male colouration and black patterning, and in other species they are supposed to be imperfect mimics, only matching male colouration. However, the underlying assumption of one female morph looking male-like is mostly based on human vision. Therefore we investigated the black patterning and colour of the three female morphs in Coenagrion puella, an imperfect mimic, using image analysis. In C. puella the blue female morph is perceived as male-like. We found that the black patterning of such females cannot be distinguished from the other female morphs, and is clearly different from males. Furthermore, the blue colour of andromorph females differs from the blue colour of males. Intriguingly, however, the red content did not differ between blue males and females.     

Colour morph related performance in the meadow grasshopper Chorthippus parallelus (Orthoptera,Acrididae)

Abstract 1. Polymorphism has been described for a number of herbivorous insects, but little is known about whether differences in body colour cause fitness differences. In Chorthippus parallelus, three main colour morphs occur, namely brown, green, and dorsally striped. 2. The present study examined colour morph abundances and morph‐related differences in body size, oviposition rate, and offspring numbers in females of C. parallelus collected in 15 montane grasslands. The study also examined the effect of plant species richness, composition, community productivity, and solar radiation on colour morph frequency and fitness. 3. The relative frequencies of the three colour morphs was 31.7% (brown), 33.1% (green), and 35.2% (dorsally striped), but the morphs were not evenly distributed across the 15 sites. 4. There was no effect of the habitat variables on the distribution of the green and the striped morph in the study sites, however 80% of the variation in the abundances of the brown morph was explained by plant species richness and composition. 5. Grasshopper size was equal among the morphs. Brown females laid significantly more egg pods than the green and dorsally striped morphs. There were no significant differences in offspring numbers among the colour morphs. 6. Body colour in C. parallelus seems to be a fitness‐relevant trait, raising the question of the evolutionary maintenance of polymorphism.     

Brown tawny owls moult more flight feathers than grey ones

The mechanisms by which melanin‐based colour polymorphism can evolve and be maintained in wild populations are poorly known. Theory predicts that colour morphs have differential sensitivity to environmental conditions. Recently it has been proposed that colour polymorphism covaries genetically with intrinsic and behavioural properties. Plumage moult is a costly and crucial somatic maintenance function in birds. We used a long‐term data set consisting of 761 observations on 307 individuals captured between 1985 and 2010 to examine differences in partial flight feather moult between grey (pale) and brown (pheomelanic dark) colour morphs of the tawny owl. We find that the brown morph consistently moult more primary flight feathers than the grey morph whereas there is no clear difference between colour morphs in the moulting of secondary feathers. Contrary to expectations, the difference in the number of moulted flight feathers between the morphs was independent of environmental conditions, as quantified by the abundance of prey. We discuss the potential physiological and behavioural causes for and costs of the observed difference in maintenance functions between colour morphs.     

Ecological mechanisms for coexistence of colour polymorphism in a coral-reef fish: an experimental evaluation

The evolution of different colour morphs and how they are maintained in animal populations is poorly understood. We investigated the mechanisms maintaining yellow and brown morphs of a coral-reef fish, Pseudochromis fuscus, at Lizard Island, on the Great Barrier Reef. Histological examination of the gonads revealed that colour morphs were not sex-limited, therefore sexual selection does not appear to promote dichromatism in this species. The field distributions of the two colour morphs were spatially segregated, limiting the opportunity for negative frequency-dependent selection to operate. Our results support another ecological mechanism of coexistence. The yellow morph occurred in deeper areas, usually close to the reef edge, where there was a proportionally high cover of live branching corals. In contrast, the brown morph occurred in shallower areas, more distant from the reef edge, that were proportionally low in live branching corals. Within these habitats, each colour morph of P. fuscus displayed a close association with similar coloured damselfishes from the genus Pomacentrus. The yellow morph was associated with predominantly yellow damselfishes (P. moluccensis and P. amboinensis) and the brown morph with darker coloured species (P. adelus and P. chrysurus). Multiple-choice experiments in the laboratory revealed that: (1) each colour morph of P. fuscus preferentially selected habitat patches occupied by damselfishes with the same colouration; and (2) differences in microhabitat use between the two colour morphs of P. fuscus were due to the presence of different coloured damselfishes in these microhabitats. P. fuscus is a predator of newly recruited damselfishes and the striking resemblance between each morph of P. fuscus and the damselfish with which it was associated, suggests that aggressive mimicry may promote coexistence of P. fuscus colour morphs.Due to an error in the citation line, this revised PDF (published in December 2003) deviates from the printed version, and is the correct and authoritative version of the paper.     

Morph‐dependent fitness and directional change of morph frequencies over time in a Dutch population of Common buzzards Buteo buteo

How genetic polymorphisms are maintained in a population is a key question in evolutionary ecology. Previous work on a plumage colour polymorphism in the common buzzard Buteo buteo suggested heterozygote advantage as the mechanism maintaining the co‐existence of three morphs (light, intermediate and dark). We took advantage of 20 years of life‐history data collected in a Dutch population to replicate earlier studies on the relationship between colour morph and fitness in this species. We examined differences between morphs in adult apparent survival, breeding success, annual number of fledglings produced and cumulative reproductive success. We found that cumulative reproductive success differed among morphs, with the intermediate morph having highest fitness. We also found assortative mating for colour morph, whereby assortative pairs were more likely to produce offspring and had longer‐lasting pair bonds than disassortative pairs. Over the 20‐year study period, the proportion of individuals with an intermediate morph increased. This apparent evolutionary change did not just arise from selection on individual phenotypes, but also from fitness benefits of assortative mating. The increased frequency of intermediates might also be due to immigration or drift. We hypothesize that genetic variation is maintained through spatial variation in selection pressures. Further studies should investigate morph‐dependent dispersal behaviour and habitat choice.     

THE STRIPED COLOUR PATTERN AND STRIPED/NON-STRIPED POLYMORPHISM IN SNAKES (REPTILIA: OPHIDIA)*

The occurrence of striped colour patterns and of striped/non-striped polymorphism systems among snakes is reviewed from literature data augmented by some personal observations. Among 1367 species, 190 were striped or had striped morphs. Of 11 families, the striped pattern was common mainly among Colubridae, presumably in relation to the active escape behaviour strategy, prevalent in this family. The striped species tended to cluster in a small number of genera. The 40 striped/non-striped polymorphism systems found, fall into five categories, according to the coloration patterns of the alternative morphs: (I) blotched (cryptic); (2) barred (or ringed); (3) plain; (4) melanistic; (5) albinistic. Most polymorphisms are presumably maintained by eco-behavioural trade-offs, depending on the category and on the habitat: The striped morph is presumed more effective in active escape and sometimes also in camouflage; the alternative morph may be more effective in camouflage, in active escape or in thermoregulation. Hence morph frequency depends on the habitat. Striped-albinistic polymorphism in Elaphe climacophora presumably depends on human protection of the albino morph.     

Infection and behavior manipulation of social wasps (Vespidae: Polistinae) by Ophiocordyceps humbertii in Neotropical forests: new records of wasp-zombification by a fungus

ABSTRACT

Ophiocordyceps is a genus comprised by entomopathogenic fungi known to infect ten orders of insects, including Hymenoptera. Amongst the nearly 250 species described in the genus, few are known to manipulate their hosts, which are most notably ants. These species cause their hosts to die in an exposed position high above the ground while grabbing and/or biting the abaxial surface of leaves or branches, which in turn optimizes the fungus spore production and dispersal. Herein, we report on 14 social wasp species belonging to four genera (Agelaia, Mischocyttarus Polybia, and Pseudopolybia) infected by Ophiocordyceps humbertii, a common wasp pathogen. This study broadens the geographic and host range for O. humbertii and provides the first record of its ability to manipulate its host.     

The pale brown allele in Cepaea nemoralis

The pale brown colour morph in Cepaea nemoralis appears to be determined by an allele at the C (colour) locus ( C ^{P B}). Pale brown is dominant to yellow, codominant with pink and recessive to dark brown. It is linked to the B locus (which controls the presence or absence of banding on the shell), but not to the U locus, which determines whether there is one band or five. In segregations of pale brown and yellow there is a significant deficiency of pale brown, suggesting that there are differences in viability between the morphs.     

Recent speciation and secondary contact in endemic ants

Gene flow is the main force opposing divergent selection, and its effects are greater in populations in close proximity. Thus, complete reproductive isolation between parapatric populations is not expected, particularly in the absence of ecological adaptation and sharp environmental differences. Here, we explore the biogeographical patterns of an endemic ant species, Cataglyphis floricola, for which two colour morphs (black and bicolour) coexist in parapatry throughout continuous sandy habitat in southern Spain. Discriminant analyses of six biometric measurements of male genitalia and 27 cuticular hydrocarbons reveal high differentiation between morphs. Furthermore, the low number of shared alleles derived from nuclear markers (microsatellites) between the morphs at their contact zone suggests the absence of recent gene flow. Mitochondrial DNA (COI) phylogenetic analysis and median‐joining networks show that the black morph is basal to the bicolour morph, with unique haplotypes recovered for each morph. Mismatch distribution analysis and Bayesian skyline plots suggest that they are undergoing different demographic changes, with the bicolour and black morphs at demographic equilibrium and expansion, respectively. Thus, our results show complete reproductive isolation between the two colour morphs as evidenced from genetic, chemical and morphological data. We suggest that these divergence events could be explained by historical vicariance during the Pleistocene, in which reproductive traits experienced strong divergent selection between the morphs initiating or culminating speciation.     

Colour biases in territorial aggression in a Neotropical cichlid fish

Discrete colour morphs have provided important insights into the evolution of phenotypic diversity. One of the mechanisms that can help to explain coexistence of ecologically similar colour morphs and incipient species is (colour) biased aggression, which has the potential to promote continued existence of the morphs in a frequency-dependent manner. I addressed colour biases in territorial aggression in a field-based study on a Neotropical cichlid fish species, Amphilophus sagittae, which has two ecologically indistinguishable colour morphs that mate assortatively. I found that A. sagittae, in particular females, were more aggressive towards models of their own colour than those mimicking colours of the other morph. Such a behavioural pattern should result in a selection regime that benefits the rarer morph, and hence could help explain how novel, rare phenotypes may avoid competitive exclusion.     

Effect of light quality and larval diet on morph induction in the polymorphic caterpillar Nemoria arizonaria (Lepidoptera: Geometridae)

The emerald moth Nemoria arizonaria (Geometridae) is bivoltine, with distinct broods of caterpillars hatching in the spring and summer. Caterpillars of the spring brood develop into mimics of oak catkins, while caterpillars of the summer brood develop into mimics of oak twigs. Previous rearing experiments showed that all caterpillars reared on oak catkins developed into catkin morphs, while all caterpillars reared on oak leaves developed into twig morphs, regardless of temperature or photoperiod. However, those previous rearing experiments did not control the colour of light perceived by the caterpillars independently of their dict. Since wavelengths of light perceived by some species of polymorphic caterpillars can influence their colour, it is possible that morph induction in Nemoria arizonaria is due to the characteristics of light reflected from yellow catkins or green leaves, rather than larval diet itself. The experiments reported here independently varied larval diet and light characteristics to determine if light quality is involved in morph induction. Only larval diet influenced morph induction, since all caterpillars reared on catkins developed into the catkin morph, and all caterpillars reared on oak leaves developed into the twig morph, regardless of whether they perceived yellow light, green light, or were raised in the dark.     

Differential predation on sexes affects colour polymorphism of the isopod Idotea baltica (Pallas)

Variable selection, including spatio-temporal variation, frequency-dependent selection and differential selection due to habitat choice, may maintain polymorphism in heterogeneous environments. We studied predation as a selective agent on colour polymorphism of the aquatic isopod I baltica. Variable predation on this species can arise from at least three sources. First, apostatic selection was studied by testing the formation of preferences on colour morphs in the perch, a common predator of I baltica. Such acquired preferences should induce apostatic selection. While our results indicate some acquired preferences, there was significant heterogeneity in the behaviour of predator individuals. Second, temporal variation in selection can arise due to habitat shift from the green algae juvenile habitat to the bladderwrack adult habitat, and the consequent change in the crypsis of the morphs. Different crypsis between sexes probably promoted high predation mortality among females in the juvenile habitat. The high rate of male mortality during the breeding period, on the other hand, was presumably due to their high mate-searching activity. Third, the sex-dependent habitat choice of I baltica leads to sexual differences in the susceptibility of morphs to predation. Predators preferred the white-spotted morph over the uniform one in males but not in females, supporting the 'dimorphic niche' hypothesis as an explanation of sexual differences in morph frequencies. Finally, no evidence was found that the colouration patterns were under sexual selection. We therefore conclude diat variable predation is the most promising explanation for the maintenance of polymorphism in I. baltica.     

Evidence for reproductive isolation between two colour morphs of cavity nesting honey bees (Apis) in south India

In south India there are two distinct colour morphs of cavity nesting honey bees: the yellow ‘Plain’ morph and the black ‘Hill’ morph which are collectively known as Apis cerana. We show that the Hill morph is associated with a widely distributed mitochondrial haplotype that is present throughout mainland populations of south east Asian A. cerana. In contrast, the Plain morph, which is apparently confined to low to moderate elevations in India and Sri Lanka, is associated with a unique mitochondrial haplotype that is not present in other cavity nesting honey bees. We further show that in a region of sympatry (Bangalore, Karnataka State) the drone mating flight times of the two colour morphs barely overlap. Combined, drone flight data and the complete separation of mitochondrial haplotypes suggest that the two morphs are reproductively isolated. The Plain morph is distinguished from the Hill morph by the first three abdominal tergites of the worker, which are completely yellow in the Plain morph, whereas in the Hill morph they are black or black with yellow patches. Although the two morphs are generally distinguishable in the field by overall colouration, microscopic examination of the first 3 abdominal tergites is preferred. Received 16 February 2006; revised 11 May 2006; accepted 23 May 2006.     

Extreme polymorphism in a Y-linked sexually selected trait

Males of the livebearing fish, Poecilia parae, exhibit one of the most complex polymorphisms known to occur within populations, whereas females are monomorphic. We describe five distinct male colour morphs and an associated size dimorphism, and demonstrate through pedigree analysis that the locus or loci controlling the male colour polymorphism is linked to the Y-chromosome. Field surveys from 1999 to 2002 of nine populations in Guyana and Suriname, South America, indicate that some morphs are consistently abundant and others are rare, implying that the colour polymorphism has important fitness consequences. By rearing offspring of field-inseminated females, we showed that the common morph is also the most successful morph in terms of reproduction. However, dichotomous choice tests show that two rare morphs are preferred by females over the common morph. These results suggest that alternative male mating strategies, sperm competition, overt male-male competition, or other processes are overriding female preferences in these populations. Furthermore, Y-linkage of the colour polymorphism in P. parae supports the hypothesis that heterogametic sex chromosomes harbour sexually antagonistic traits beneficial to the heterogametic sex.     

Colour polymorphism in the intertidal snail Littorina rudis Maton

The tictors affecting the variation of shell colour morph frequencies of the intertidal snail Littorina rudis Maton have been examined using ordination and correlation techniques. The major gradient underlying variation in shell colour is related to habitat type and structure. Dark, patterned shells are characteristic of cliff and salt marsh habitats whilst light, unpatterned shells reach high frequencies on boulder shores. Colour morphs do not differ significantly in shell thickness and between-shore variation in colour morph frequencies cannot be directly attributed to habitat dilterences in the risk of shell injury, but to other factors associated with habitat type and structure, e.g. parasitism. It is suggested that the maintenance of shell colour polymorphism in L. rudis is probably mediated by selection on pleiotropic characters rather than shell colour alone.     

Incipient reproductive isolation between two morphs of Drosophila elegans (Diptera: Drosophilidae)

Drosophila elegans is a flower-breeding species occurring in tropical and subtropical regions of Asia. Two morphs, brown and black, are known in this species. The brown morph is recorded from southern China, Philippines, Indonesia and New Guinea, while the black morph is from the Okinawa islands and Taiwan. The present crossing experiment suggests that the difference of body colour between them was due to alleles on a single locus or closely linked loci on an autosome; F₁ hybrids exhibited intermediate body colour. Female choice tests revealed asymmetrical premating isolation between the brown and black morphs; isolation indices ranged from 0.55 to 0.83 in the tests using females of the black morph (deviation from random mating was significant), but from — 0.03 to 0.50 in the tests using females of the brown morph (deviation from random mating was insignificant). However, body colour was not used as a criterion of mate choice by females. A weak and asymmetrical postmating isolation was also observed between the brown and black morphs; viability was lowered in F₂ progenies of crosses between females of the brown morph and males of the black morph. No premating or postmating isolation was observed between geographic strains of each morph. Under irradiation, body temperature was higher in the black morph than in the brown morph. On the other hand, no significant difference was observed in tolerance to cold, heat and desiccation between the brown and black morphs.     

Endocrine differences among colour morphs in a lizard with alternative behavioural strategies

Alternative behavioural strategies of colour morphs are expected to associate with endocrine differences and to correspond to differences in physical performance (e.g. movement speed, bite force in lizards); yet the nature of correlated physiological and performance traits in colour polymorphic species varies widely. Colour morphs of male tawny dragon lizards Ctenophorus decresii have previously been found to differ in aggressive and anti-predator behaviours. We tested whether known behavioural differences correspond to differences in circulating baseline and post-capture stress levels of androgen and corticosterone, as well as bite force (an indicator of aggressive performance) and field body temperature. Immediately after capture, the aggressive orange morph had higher circulating androgen than the grey morph or the yellow morph. Furthermore, the orange morph maintained high androgen following acute stress (30 min of capture); whereas androgen increased in the grey and yellow morphs. This may reflect the previously defined behavioural differences among morphs as the aggressive response of the yellow morph is conditional on the colour of the competitor and the grey morph shows consistently low aggression. In contrast, all morphs showed an increase in corticosterone concentration after capture stress and morphs did not differ in levels of corticosterone stress magnitude (CSM). Morphs did not differ in size- and temperature-corrected bite force but did in body temperature at capture. Differences in circulating androgen and body temperature are consistent with morph-specific behavioural strategies in C. decresii but our results indicate a complex relationship between hormones, behaviour, temperature and bite force within and between colour morphs.     

Testing the role of coadapted genes versus bet-hedging for mating strategies in colour polymorphic pygmy grasshoppers

Recent investigations of mate choice indicate that the genetic effect of sires on offspring fitness may depend on the interaction between maternal and paternal genotypes and the environmental conditions experienced by the offspring. Alternative colour morphs of the pygmy grasshopper, Tetrix subulata , represent ecological strategies that differ in body size, life history, thermoregulatory behaviour, and habitat selection. The hypothesis that selection promotes behaviours maintaining coadapted gene complexes predicts individuals to mate assortatively with respect to colour morph. On the other hand, the bet-hedging hypothesis predicts that the temporal variability of the environment inhabited by these animals may select for disassortative mating behaviour resulting in heterogeneous offspring. To distinguish between these competing hypotheses, we investigated mating behaviours using dual-choice experiments. Our results were not in agreement with the prediction of assortative mating but suggest instead that matings were random with regard to colour morph. Polyandry was common, and females mated with the second male regardless of whether the first mating was assortative or disassortative. Polyandry also was equally frequent among females in triads in which the two males belonged to different colour morphs as in triads where both males belonged to the same colour morph. A field experiment confirmed that polyandry occurred also among free-ranging individuals, and uncovered variation in mating success among male colour morphs, probably due to indirect effects of coloration on activity or habitat use. The consequences of this random and polyandrous mating strategy for the evolutionary dynamics of the colour polymorphism remain to be explored.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 491–499.